1. Field of the Invention
The present invention relates to a color toner, particularly to a negative charge color toner composition for electrostatic charge development.
A static electron printing method and an electrophotography method are well-known methods of developing an electrical latent image with a color toner to form a visual image. Generally, in each of these methods, an electrical latent image is first formed on a photosensitive material having photoconductivity by the use of photoconductive substances and various means, and the thus formed latent image is then developed with a toner to obtain a visual image, or alternatively a dust figure is first transferred to a paper sheet or the like, if necessary, and it is then fixed by heating, pressing or a solvent vapor, thereby obtaining a visual image.
In order to obtain a multicolor image, an original is first subjected to exposure through a color separation filter, and the above-mentioned process is then repeated plural times by the use of color toners of yellow, magenta and cyan, whereby the desired color image is formed thereon.
As the toner for developing the electrical latent image, particles have heretofore been used which may be prepared by grinding, to a size of 0.1 to 50 .mu.m or so, a binding resin such as polystyrene in which a colorant is dispersed. This kind of color toner is usually mixed with a carrier material such as glass beads or iron powder, and the thus produced color toner is used for the development of the electrical latent image.
2. Description of the Prior Art
Color toners for the development of electrical latent image must have various physical and chemical characteristics. However, most of the known color toners have the following drawbacks or do not satisfy the following requirements necessary for the color toners:
(1) The frictional electricity properties of the color toners are inversely affected by temperature change.
(2) When continuously used and repeatedly developed, color toner particles collide with carrier particles, and these particles and the photosensitive plate to which they attach themselves deterorate mutually. Consequently, a change in color density takes place or the density of the background heightens, which impairs the quality of the copies produced therefrom.
(3) When the amount of the color toner on the surface of a photosensitive plate having a latent image is increased, with the intention of heightening the density of a copy image, the background density usually also rises, with the result that the so-called fog phenomenon occurs.
(4) Since many colors are superposed upon one another, it is necessary that the color toners have good transparency.
(5) The method respective color toners are required to be excellent in miscibility.
(6) For the faithful reproduction of an original, spectral reflection properties must be good.
Most of the known color toners have one or more of the above-mentioned disadvantages or do not meet all of these requirements and thus improvement is desired.
The use of 1-amino-4-hydroxy- and 1,4-diaminoanthraquinones to provide a magenta color toner is disclosed in commonly assigned U.S. Application Ser. No. 291,896, filed 12/29/88, and the prior art discussed therein.
We have found that a certain kind of anthraquinone derivative provides a magenta color for color toners and has excellent melt miscibility, stable frictional electricity properties, high light-fastness and good transparency. Furthermore, it has been also found that when a negative charge color toner composition for electrostatic charge development containing the anthraquinone derivative as a dyestuff is utilized in performing duplication, a fog-free and sharp magenta color image can be obtained in a stable density even by repeated development for continuous duplication and the light-fastness of the thus obtained color image is also good.
An object of the present invention is to provide a novel magenta color toner composition for the electrostatic charge development containing a compound represented by the general formulae (I) and/or (II) as a dyestuff.